Andries - I'm not sure I follow YOU here. VOCs = "volatile organic compounds" which include volatile hydrocarbons like gasoline (the fuel). Also includes hydrocarbon emissions from vehicle exhaust and solvent emissions from industry along with many other sources.

For the purposes of atmospheric chemistry, VOCs are the vapors (gas phase) of these substances. For example, if you spill gasoline while filling up your law mower, that gasoline quickly evaporates, and those vapors drift off as "VOCs".


Since VOCs consist of a myriad of different volatile compounds, studies can be conducted to "apportion" those VOCs to a source (call "source apportionment" studies). VOCs like gasoline have a different ambient "signature" than those VOCs from industrial solvents (for example). Sampling the atmosphere in specific locations can determine not only the total concentration of VOCs, but concentrations of individual VOC components (e.g., butane, octane, nonane, etc.)

Ambient NOx levels can be determined by dedicated "NOx detectors". Of course, since NOx = NO + NO2, "source apportioning" of NOx is difficult since there are no unique signatures from different sources of NOx.


That I can't answer, since these "weekend ozone effect" studies have established a negative correlation between ambient NOx concentrations and ambient ozone levels (i.e., lower ambient NOx levels result in higher ambient ozone levels). Most of these weekend ozone effect studies have been published in peer-reviewed scientific journals, so it's a little difficult to ignore (although the regulators seem to be doing just that).

Again, it's not that NOx shouldn't be regulated (with the ultimate goal of zero anthropogenic NOx), but the regulators need to be careful of how they approach emission regulations (i.e., the approach of reducing VOC and CO emissions relatively more than NOx emissions is what should be considered rather that the inverse which is what the current regulations achieve).

 

I have no data for diesels or non-Prius vehicles. I wish we did. Rather than those EPA numbers, I would prefer a set of MPG vs miles per hour charts so we could could see what these vehicles do at different speeds, temperatures and driving profiles. The numbers don't do it for me.

About the chart, you'll notice there is distinct fall off in MPG for the 2000-03 Prius at 70 mph and the NHW20 shows a similar drop off between 85-90 mph. Due to the different control laws managing the transaxle, I believe these are both due to MG1 rpm management. The NHW11 tries to keep MG1 rpm under 6.5k rpm and the NHW20 has a stronger one that can go to 10k rpm.

Bob Wilson

 

Bob - Green Car Congress referenced a study from Europe that measured mpg vs. speed of many different vehicles/technologies a few years ago (see http://www.greencarcongress.com/2006...onsumptio.html ). There's a link to the actual article, but that article is in German.

Not sure if this is what you are looking for or if it's representative of U.S. vehicles, but I thought I'd mention it...

 

Thx, I think it understand it better now. Basically don't just focus on just a single area, but all of them when looking at a car's emissions.

So going back to the elemnts measued by the EPA tests it would then be best to pick a vehicle with lowest score in all the categories? I understand there are other things that needs to be done to control air pollution, but in this case we are looking at car selection to reduce air pollution.

So in this case looking at the results of the 3 vehciles I mentioned earlier, the Camry Hybrid would be the cleanest by a mile. I have not seen EPA data on the new VW diesels scheduled for the US, the cleanest EPA tested diesel I could find was the MB E320 BlueTec. To be honest the Bluetec results look horrible compared to the hybrid, I realize it is a diffferent class vehicle but still.

I surely hope the VW diesels fair much better than that to be considered clean in my book. And I guess that is my point, I would like to see the test results reflect the clean "advertising" before I bite.

Thanks for the information regarding the different elements to look at and not to get hung up on a few parameters.

Results listed below.
TDi results were:
CO - 0.03
HC-NM+NOX-COM - 0.7483
NMOG - 0.0141
NOX - 0.31
PM - 0.046

4Cyl Camry
CO - 0.21
HC-NM+NOX-COM - 0.077
NMOG - 0.0198
NOX - 0.016
PM - NA

Camry Hybrid
CO - 0.03
HC-NM+NOX-COM - 0.008
NMOG - 0.004
NOX - 0.001
PM - N/A

E320 BlueTec
CO - 1.326
HC-NM+NOX-COM - 0.169
NMOG - 0.0327
NOX - 0.052
PM - 0.0028

 

Generally, although as I've mentioned, VOCs (aka NMHC or NMOG as exhaust emissions) are relatively more important than NOx from an air quality (pollution) perspective, per unit mass.


I agree that the E320 BLUETEC emission profile is pretty bad, and the lower NOx emissions at the expense of higher CO and HC emissions is NOT a good trade off in my opinion (the certified CO and NMHC emissions for the 2005 E320 CDI were 0.1 g/mi and 0.0 g/mile respectively; certified NOx emissions were 0.39 g/mi).

The 2008 Jeep Grand Cherokee CRD (diesel) has the following certified emission profile:

CO - 0.0
CO (US06) - 0.0
CO (SC03) - 0.0
HC-NM - 0.006
NOx - 0.4
PM - 0.0

In my opinion, this is a "better" emission profile than the BLUETEC in spite of the much higher NOx emissions.

There's no doubt that the current gas hybrids have extremely low direct emissions. One point to keep in mind however is the VOC emissions from the supply chain of gasoline. These are not reflected in the Tier 2 or LEV II emission regulations. This is a reason why I would find diesel hybrids (DHEV) very appealing.

 

well, thats great, the diesel jetta gets 41 on the highway. i just pulled an 82 mpg tank with my insight. sorry, i just can't work up much enthusiasm for half the mileage. granted, my car only has 2 seats, but i just use it to commute and run errands 15,000 miles a year.

 

Apples and oranges. With a 385-lb. load limit, the Insight can barely even accomodate two adults, let alone their cargo. It is an extremely niche-appeal car that does not serve the needs of a vast majority of Americans. The Jetta is a much larger and heavier car, with a much larger and more powerful engine, and the fact that it can comfortably hold four adults and their cargo and still get nearly 50 MPG on the highway is quite commendable, at least in my book.

 

yeah, i know its at its best as a commuter car. and thats how i use it. however, it does quite well with two adults (500 lbs) and a bunch of camping gear in the back. could use slightly stiffer rear springs though. that 385 lb load limit was pulled out of the air for the initial epa testing. they had to use some number, and thats what they came up with.

i guess i tend to go to extremes. i used to commute in a jeep grand wagoneer. 5000 lbs of iron, 11-12 mpg. now i haul around about 1900 lbs of car (+ me). i guess not everybody can afford a very special-purpose car. i still use the wag to pull the boat. but i still see almost everybody hauling around WAY too much car (or truck. or suv) for everyday use.